A communication system is formed, at a minimum, of a transmitter and a receiver interconnected by a communication channel. The communication system is operable at least to transmit communication signals, having an informational content, generated at, or applied to, the transmitter. The communication signals are transmitted to the receiver upon the communication channel. The receiver is operable to receive the transmitted, communication signal and to recreate the informational content of the communication signal.
A radio communication system is a communication system in which the communication channel is formed of one or more frequency bands of the electromagnetic frequency spectrum. A transmitter operable in a radio communication system generates a communication signal of characteristics permitting its transmission upon the communication channel, and the receiver operable in the radio communication system is operable to receive the communication signal transmitted upon the communication channel.
A radio communication system is advantageous for the reason that a fixed, or hard-wired, connection is not required to form the communication channel extending between a transmitter and a receiver. Communication can be effectuated between remotely-positioned transmitters and receivers without the need to form the hard-wired or other fixed connections therebetween.
A cellular communication system is a type of radio communication system. When the infrastructure, hereinafter referred to as the network, of the cellular communication system is installed in a geographical area, a subscriber to the cellular system is generally able to communicate telephonically in the system when positioned at any location in the geographical area encompassed by the system.
Cellular communication networks have been installed throughout significant portions of at least many of the world's population centers. Large numbers of subscribers to cellular communication systems formed of such cellular networks are able to communicate telephonically when positioned in areas encompassed by such cellular networks.
However, in some areas, terrestrial-cellular communication networks might not be installed or might not be commercially viable. For terrestrial-cellular communication networks which have already been installed, some may have been constructed pursuant to various different standards. A user terminal operable in one of the cellular communication systems may not be operable in others of the cellular communication systems.
Therefore, even in an area in which a cellular communication network has been installed, a user might not be able to communicate by way of the cellular communication network if the user attempts to utilize a user terminal constructed to be operable only with another one of the cellular communication networks.
Satellite-cellular communication systems have been proposed which, when implemented, shall permit a user, utilizing a user terminal operable therein, to communicate telephonically by way of the satellite-cellular communication system when positioned at almost any location. By transmitting down-link and up-link signals between a satellite-based transceiver and the user terminal, telephonic communication shall be possible between the user terminal and the satellite-based transceiver. By effectuating additional communication links between the satellite-based transceiver and a ground station, the user of the user terminal shall be able to communicate telephonically with another party by way of the ground station and the satellite-based transceiver.
In both satellite and terrestrial cellular communication systems, when a call is to be placed to a user terminal, a network station in a satellite-based system, or a base station in a terrestrial-cellular base system, transmits a paging signal to the user terminal. The paging signal includes the equipment identifier (EIN) of the user terminal and a random reference number.
Upon receipt of the paging signal, the user terminal sends to the base/network station a response signal base upon the random reference number. In a similar manner, the base/network station forms the same response signal and compares it to the user terminal response signal. These signals must substantially correlate in order for the base/network station to uniquely identify or authenticate the user terminal. Similarly, in both satellite and terrestrial cellular communication systems, when a user terminal is originating a call, an access request signal is sent to the base/network station from the user terminal. Typically the access request signal includes a call establish cause, the dial number information, and a random reference number.
Upon receipt of the access request signal, the base/network station sends to the user terminal a response signal based upon the random reference number. The user terminal forms the same response signal and compares it to the base/network station response signal. These signals must substantially correlate for call establishment to proceed.
Because communication systems are being developed in manners which attempt to minimize the bandwidth required to communicate between the base/network station and the user terminal, the available bandwidth for communication between the base/network station and the user terminal on the forward as well as the reverse channels is often limited.
When the paging data or the access request data being transmitted exceeds the available limited bandwidth, the limited bandwidth may prevent adequate paging communication or access request communication between the user terminal and the base/network station, thereby hindering proper communication.
Another problem encountered with the access request signal occurs as discussed above, the access request signal transmitted by the user terminal to the base/network station when originating a call typically includes a call establishment cause, the dial number information, and a random reference number. The number of bits of information used for the random reference number varies from two to five bits.
Typically five bits are used for random reference for the calls that occur most frequently or are of high priority, such as originating calls or emergency calls. Five bits are used to reduce the probability that two phones have an identical random reference number. In contrast two bits are typically used for the types of call which occur least frequently.
For the above mentioned problems, what is needed therefor, is a manner by which to reduce the size of the paging and access request signals to be transmitted between a base/network station and a user terminal to ensure that the signals will fit a limited bandwidth. What is also needed, is an access request signal of a fixed length or fixed format.
It is in light of this background information related to communications pursuant to a radio-telephonic communication system, such as a satellite-based or terrestrial-based cellular communication system, that the present invention has been developed.